Electric motors, which operate by converting electrical energy into mechanical energy, are used to power many labor-saving devices. A typical electric motor can include an armature, a stator, a commutator, and a plurality of brushes. The plurality of brushes, which can include a first brush and a second brush, can pass current from a power supply to the commutator. In a typical DC motor, the first brush can act as a negative terminal and the second brush can act as a positive terminal (or vice versa) such that current can be conducted through the commutator. The first brush (or common brush) can be a current conducting brush mounted in a stationary position relative to the commutator. The second brush can be a current conducting brush capable of being mounted in a plurality of positions. In an alternative configuration, the second brush can be mounted in a fixed position and there can also be a third brush mounted in a fixed position. In such a configuration, a switching circuit can be used to ensure that only one of the second brush and the third brush is able to conduct current at a given time. Similarly, there can also be a fourth brush, and so on.
In an electric motor with only two brushes, varying the position of the second brush relative to the first brush and/or relative to the commutator can facilitate different optimal electric motor speed and torque ranges or modes. For example, a low speed, high torque operating mode can be facilitated by positioning the second brush such that it is annularly spaced 180 degrees from the first brush. Similarly, higher speed, lower torque operating modes can be facilitated by positioning the second brush such that it is annularly spaced less than 180 degrees from the first brush. In an electric motor with third, fourth, etc. brushes, different operating modes can be facilitated by manipulating a switching circuit to control which of the second, third, fourth, etc. brushes is capable of conducting current at a given time.
To ensure that an electric motor does not break down or overheat, an amount of operational current supplied to the electric motor should correspond to the optimal operating mode dictated by the position of the brushes that are conducting the current. If the brushes are positioned such that the electric motor is in a low speed operational mode, a controller should provide an amount of current required for low speed operation. Supplying a high speed operational current to an electric motor that is set up for low speed operation can cause the electric motor to overheat and/or break down. Likewise, if the position of the brushes dictate that the electric motor is in a high speed operational mode, the controller should provide an amount of current required for high speed operation such that the electric motor operates efficiently and safely.
In general, a user action informs the controller of an optimal operating mode of an electric motor corresponding to a present brush configuration. The user action can include flipping a switch, pressing a button, turning a knob, etc. If the user fails to correctly inform the power supply controller of the current required for optimal operation as dictated by the brush configuration, the electric motor can run inefficiently and/or be damaged. Thus, there is a need for an electric brush motor in which a position of a current conducting brush can be automatically detected without a user action. Further, there is a need for an electric brush motor in which a required operational current can be automatically supplied based on the detected position of the current conducting brush.